Comets and asteroids
A ball of icy rock that follows an elliptical orbit around the Sun. are balls of rock and ice. The ice melts as the comet gets closer to the Sun, producing its 'tail'. They have highly elliptical or eccentric orbits.
Many comets pass far outside of the solar system.
Asteroids
A rock in space. Asteroids orbit the Sun but some may cross the Earth's orbit, producing a small risk of collision. are large rocks that are mainly found in a belt between Mars and Jupiter. A dwarf planet called Ceres can be found in this asteroid belt. The rocks in the asteroid belt may be remnants of a planet that failed to form due to the strong gravitational attraction of Jupiter.